Physics 4.4 (Waves) Flashcards
How do waves transfer energy and what is the difference between longitudinal and transverse waves?
-Waves transfer energy from one place to another without transferring matter
-Longitudinal waves vibrate parallel to their direction of travel and examples are sound waves and P waves
-Transverse waves vibrate perpendicular to their direction of travel and examples are electromagnetic waves
What are the wavelengths of EM radiation?
-Radio: >10^3m
-Microwave: >10^-2m
-Infrared radiation: >10^-5m
-Visible light: >10^-6m
-Ultraviolet: >10^-8m
-X-rays: >10^-10m
-Gamma rays: >10^-12m
Draw a circuit to show how x-rays can be produced?
-X-rays are produced by firing high energy electrons at a copper anode
What are progressive waves?
-Waves that transfer energy away from a light source
What are two ways we can display a wave
-As a snapshot of the wave profile as the disturbance moves outwards with distance against displacement
-The oscillation of an individual particle with time against displacement
What is wavelength, period and frequency of a wave?
-Wavelength is the distance between two adjacent identical points on the oscillation, measured in meters
-Period is the amount of time it takes to complete one pattern of oscillation at any point, measured in seconds
-Frequency is the number of oscillations per unit of time, measured in hertz one oscillation per second
What is the amplitude of a wave?
-Amplitude is the distance between the rest position and a peak or trough
What is the phase difference of a wave?
-If two waves have the exact same pattern of oscillation they are said to be in phase.
-Phase difference is the shortest difference between two points on diffferent waves that are in phase
-It can be measured in degrees with 180 degrees representing half a wave or in pie with pie being half a wave and 2 pie as in phase.
What is the wave equation and the speed of light and sound?
-V=fλ
-Speed of light= 3*10^8 m/s
-Speed of sound= 340m/s
What is the equation for the intensity of a wave? and how is amplitude proportional to intensity?
Intensity=power/area
Intensity is proportional to the square of amplitude for a progressive wave
What does the distance between the wavefronts represent in a wavefront diagram?
-Wavelength
When is a wave refracted and what can be observed?
-When a wave moves from one material to another which has different optical densities
-The wave will change its speed and if the wave doesn’t pass into the object perpendicular to its surface you will notice a change in the direction
What is the equation for Snells law?
How can you determine the refractive index of a material?
1.Place a semi circular block on a piece of paper and trace around it, use a light ray to point a beam of light at the block
2.Trace the rays at different angles of incidences to the normal and use a protractor to find both angle of incidence and angle of refraction (θ₁ and θ₂)
3. Draw a graph of Sin θ₁ on Y-axis and Sin θ₂ on x-axis
What is the refactive index of air and glass?
Air:1
Glass:1.5
What is the diffraction of a wave?
-The spreading out of a wave after passing around an obstacle or through a gap, when the gap width is the same size as the wavelength of the wave
What is interference?
-When two or more diffracted wave patterns overlap and interfere with each other creating an interference pattern
What are the properties of electromagnetic radiation?
-Can all travel through a vacuum
-Have both a magnetic and electrical wave at right angles to each other
-Travel at the speed of light
-Can all be reflected, refracted, and diffracted
-Can all Demonstrate interference
-Can all be polarised
What is ionising radiation and what are the different types of ultraviolets?
-Ultraviolet, x-rays and gamma radiation are all ionising radiation this is because they have the photon energy to knock electrons from the shells of atoms.
-Ultraviolet has three types: ultraviolet A (causes tanning), ultraviolet B (causes damage such a sunburn and skin cancer) and ultraviolet C (filtered out by atmosphere) and are all emitted by the sun
What is an unpolarised wave, a plane polarised wave and a polarising filter?
-An unpolarised wave can have an electric field in any number of planes
-A plane-polarised wave is a wave that has fields in only one plane
-A polarising filter causes an unpolarised wave to have oscillating waves in only one plane
(Exam Question) Describe how you can demonstrate in a laboratory that reflected light is plane-polarised?(2marks)
-Use a polaroid/polarising filter (1mark)
-Rotate the filter and the reflected light should change intensity (1mark)
What will happen if you have a source of light and a polarising filter infront of it and then you rotate another polarising filter through 360 degrees?
-As the second filter is rotated from 0-90 degrees the light intensity decreases until it reaches 90 degrees where no light will be able to pass through light intensity then increases back up to 180 degrees
-This is because the second polarising filter is decreasing the amplitude of the wave when it rotates.
What is the equation for refractive index?
n= speed of light in vacuum/speed of light in material
How do polarising glasses cut out glare?
-Light that has been reflected can be partially polarised, more light in the direction of oscillation than other directions, polarising glasses can cut out this light reducing glare
What is total internal refraction?
- When a wave hits the material with an angle of incidence equal to the critical angle it causes the refracted wave have an angle of refraction of 90 and move along the boundary.
What happens when a wave hits a material below or above the critical angle?
-Lower than the critical angle refraction will occur but there will also be a weak reflected ray
-If we increase the angle of incidence above the critical angle only reflection will take place
What is an equation involving critical angle and refractive index?
sinC=1/n
What does the principle of superstition state? and what are the conditions?
-When two or more of the same type of wave meet the resultant wave can be found by adding up the displacements of the individual waves
-The waves must maintain a constant phase difference (coherent)
What is constructive and destructive interference?
-Constructive when two waves with the same amplitude that are in phase meet the resultant wave will be twice of the individual waves
-Destructive interference when two waves that are antiphase meet they cancel each other out and the resultant wave has an amplitude of zero
What is the difference between path difference and phase difference?
-Both refer to the distance between two waves
-Path difference is measured in wavelength and phase difference pie (a quarter of a wave is wavelength over 4 or pie over 2)
What does coherent mean?
-A pair of waves that have a constant phase difference
Does the difference between constructive and destructive patterns increase or decrease with lower frequencies
Increases
Describe Thomas Youngs double slit experiment?
1.Monochromatic light waves leave the light at source x
2. They reach the single slit and diffraction occurs at the slits at the same distance as their wavelength
3.They reach the double slit at Y and diffraction occurs, the waves come from the same source so must be coherent
4. Diffracted waves overlap and interfere
5. This creates fringes where there will be no light and light due to constructive and destructive wave interference
What are the two equations for wavelengths of a double slit experiment?
What was the purpose of Thomas Youngs double slit experiment?
-To work out the wavelength of light
How would you increase the brightness and sharpness of maxima in the youngs double slit experiment
-Increase the number of slits the light has to pass through
What are nodes and antinodes?
-Nodes are points on a stationary wave where there is no displacement and antinodes are points where the displacement is maximum
What is the fundemental mode of frequency?
- When the length of the string is half the wavelength you produce a wave with its lowest possible fundamental frequency, waves with higher frequencies can be produced called harmonics
How can you use an oscilloscope to find the speed of sound?
1.Strike the tuning fork and slowly move the water out until the sound is the loudest to get fundamental frequency(when the sound is loudest at its minimum length), this length is equal to a 1/4 of the wavelength
2.Keep moving water out until sound becomes loud again this distance is 1/2 of the wavelngth mulitply by 2 and the frequency of the tuning fork to get the speed of sound
What are the equations involving frequency, time period and time base?
What is the equation for Malus’ law
